Wood and utility-type golf club heads generally include a front or striking face, a crown, a sole, and an arcuate skirt including a heel, a toe, and a back. The striking face interfaces with and contacts the golf ball. A plurality of grooves, sometimes referred to as “score lines,” may be provided on the face to assist in imparting spin to the ball and for decorative purposes. The crown is generally configured to have a particular look to the golfer and to provide structural rigidity for the striking face. The sole of the golf club contacts and interacts with the ground during the swing.
With a high percentage of amateur golfers constantly searching for more distance on their shots, particularly their drives, the golf industry has responded by providing golf clubs specifically designed with distance and accuracy in mind. The head sizes of wood-type golf clubs have increased, allowing the club to possess a higher moment of inertia (MOD, which translates to a greater ability to resist twisting on off-center hits. Generally, as wood-type club head becomes larger, its center of gravity will be moved back away from the face and further toward the toe, resulting in hits flying higher and further to the right than expected (for right handed golfers). Reducing the lofts of the larger head clubs can compensate for this. Because the center of gravity is moved further away from hosel axis, the larger heads can also cause these clubs to remain open on contact, thereby inducing a “slice” effect (in the case of a right-handed golfer the ball deviates to the right). Offsetting the head and/or incorporating a hook face angle can help compensate for this by “squaring” the face at impact, but often more is required to eliminate the “slice” tendency.
Another technological breakthrough in recent years to provide the average golfer with more distance is to make larger head clubs while keeping the weight constant or even lighter by casting consistently thinner shell thicknesses and using lighter materials such as titanium, magnesium, and composites. Also, the faces of the clubs have been steadily becoming thinner, because a thinner face will maximize what is known as the coefficient of restitution (COR) from impacts with golf balls. The more a face rebounds upon impact, the more energy is imparted to the ball, thereby increasing the resulting distance that the ball travels.
Known methods to enhance the weight distribution of wood-type club heads to help reduce the club from being open upon contact with the ball usually include the addition of weights to the body casting itself or strategically adding a weight element at some point in the club. Efforts to incorporate weight elements into the wood-type club head are discussed in the patent literature. For instance, U.S. Pat. No. 7,186,190 discloses a golf club head comprising a number of moveable weights attached to the body of the club head. The club head of the '190 includes a number of threaded ports into which the moveable weights are screwed. Though the mass characteristics of the golf club may be manipulated by rearranging the moveable weights, the cylindrical shape of the weights and their placement within the golf club body necessarily moves a significant portion of the mass toward the center of the club head, which may not maximize the peripheral weight of the club head or the MOI. Moreover, most cylindrical weight members are attached to the club head via threaded engagement; during normal play, the cylindrical weights may rotate and become unintentionally disengaged from the club head.
As previously stated, a concern for higher handicap golfers is the tendency to “slice,” which in addition to deviating the ball to the right also imparts a greater spin to the ball, further reducing the overall ball distance. To reduce this tendency, the '190 patent teaches the placement of weight elements directly into the club head. The placement of weight elements is designed so that the spin of the ball will be reduced, and also a “draw” (a right-to-left ball flight for a right-handed golfer) will be imparted to the ball flight. This ball flight pattern is also designed to help the distance-challenged golfer because a ball with a lower spin rate will generally roll a greater distance after initially contacting the ground than would a ball with a greater spin rate.
Alternative approaches for moving the center of gravity of a golf club head rearward and downward in the club head utilize composite structures. These composite structures utilize two, three, or more materials that have different physical properties including different densities. By positioning materials that provide the desired strength characteristics with less weight near the crown or top line of a golf club head, a larger percentage of the overall weight of the golf club head is shifted towards the sole of the club head. This results in the center of gravity being moved downward and rearward. This approach is advantageously applicable to muscle back iron clubs or fairway woods, as this will help to generate loft and power behind and below the ball. An example of this type of composite club head is shown in U.S. Pat. No. 5,720,674. The club head of the '674 patent comprises an arcuate portion of high-density material bonded to a recess in the back-skirt. Because composite materials like those found in the '674 club head must be bonded together, for example by welding, swaging, or using bonding agents such as epoxy, they may be subject to delamination or corrosion over time. This component delamination or corrosion results in decreased performance in the golf club head and can lead to club head failure.
Though many methods of optimizing the mass properties of golf club heads exist, there remains a need in the art for a golf club head comprising at least a movable weight a having secure attachment means and a low-profile such that the weight does not protrude into the center of the club head and negatively affect the location of the center of gravity.